Twin scroll turbocharger configurations may be used in turbocharged engines. A twin scroll turbocharger configuration may separate an inlet to a turbine into two separate passages connected to exhaust manifold runners so that exhaust from engine cylinders whose exhaust gas pulses may interfere with each other are separated.
For example, on an I4 engine with a cylinder firing order of 1-3-4-2, exhaust manifold runners 1 and 4 may be connected to a first inlet of a twin scroll turbine and exhaust manifold runners 2 and 3 may be connected to a second inlet of said twin scroll turbine, where the second inlet is different from the first inlet. Separating exhaust gas pulses in this way may, in some examples, result in an increase in efficiency of exhaust gas delivery to a turbine.
However, the inventors herein have recognized that under some engine operating conditions separating exhaust gas pulses as described above may reduce an efficiency of exhaust gas delivery to a turbine. For example, the inventors herein have recognized that under certain engine operating conditions, e.g., high speed and high load conditions, separating exhaust gas pulses as described above may result in an increase in backpressure and pumping work due to, for example, an increase in exhaust gas enthalpy.
The inventors herein have also recognized that high pressure exhaust gas recirculation (EGR) may be used during some conditions in engines with a twin scroll turbocharger configuration. The inventors herein have recognized that if exhaust gas is taken off the exhaust feeding a twin-scroll turbine, pressure pulsations of the exhaust gas driving the turbine may be disadvantageously dampened.
In one example approach, a method for operating an engine with a twin scroll turbine and an EGR system comprises: during a first condition, fluidically separating the scrolls of the twin scroll turbine and operating said engine with reduced EGR; and during a second condition, fluidically combining the scrolls of the twin scroll turbine and operating said engine with increased EGR.
In this way, an engine including a twin scroll turbocharger configuration may be operated using the twin scroll feature in a first mode, and effectively operated using a single scroll to drive the turbine in a second mode, depending on various engine operating conditions.
Additionally, when high pressure EGR is used in an engine with a twin scroll configuration, the exhaust gas supplying the EGR system may be taken off both sides of the twin scroll inlet to the turbine. In this way, dampening and/or unevenness of pressure pulsations of exhaust gas driving the turbine may be reduced.
For example, by opening up the high pressure EGR system and communication between scrolls of a twin scroll turbine during certain engine operating conditions, e.g., during high speed/high load conditions, the high pressure EGR may be used for enrichment reduction and the turbine inlet communication may reduce back pressure and increase a horsepower capability of the engine.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.